This invention relates to preparing crystalline substrates useful for optical waveguides.
Crystalline LiNbO3 and LiTaO3 are used in optical waveguides. Integrated optic circuits based upon such optical waveguides are useful in various electrooptical devices including, e.g., fiber optic gyros (FOGs), photonic switching devices, and intensity/phase modulation systems. A variety of methods exist for fabricating LiNbO3 and LiTaO3 integrated optic circuits. Examples of these methods include localized diffusion of hydrogen into a LiNbO3 or LiTaO3 substrate, and proton exchange with the lithium present in the LiNbO3 or LiTaO3 substrate. These methods alter one or more refractive indices (e.g., the extraordinary and ordinary refractive indices) of the substrate in the region containing the diffused hydrogen to produce an optical waveguide.
During fabrication of the optical waveguide, protons replace the lithium atoms of the crystal structure. These protons are relatively small in comparison to the lithium atom and thus tend to move about the crystal structure of the waveguide. As a result, optical waveguides, the refractive index, and the region of guide itself tend to drift over time, which alters the output intensity of the waveguide. The waveguides must then be reset or recalibrated to correct for drift.